I was reading Bastard Sword, a blog I hadn’t come across before, and he was discussing a the-skies-are-falling article in the Guardian about Argentina’s "ecological disaster" due to Roundup Ready soybeans, and the follow-up article in the Telegraph debunking the hell out of the Guardian article and the New Scientist hitjob that inspired it.
I don’t have any real problems with the Telegraph article, or his take on the whole situation. What did catch my eye, however, was the claim that the RR soybean crop was screwing up the soil ecology of Argentina’s croplands, and how both the post and the article dismissed this claim without explaining why it’s not credible.
Soybeans are a legume crop. Like most legumes, the soybean plant creates soil cultures which produce lots of excess nitrogen. This helps nutrient-drained fields recover from previous industrial use. This is why soybeans are used in rotation with highly demanding crops like cotton, corn, barley or wheat. Corn or maize is particularly fertilizer-dependant, especially on nitrogen. (Of course, corn produces something like three to four times the yield of soybeans, all other factors being equal. Wheat and barley produce half again to twice the yield volume of soybeans.) Soybeans actually replenish nitrogen to the soil. And that’s part of the problem, if you don’t rotate the soybeans with something else.
The problem with continuously planting soybeans without rotation is that soybean fields are susceptible to nematode infestations which do a real number on productivity. Nematodes love that nitrogen-rich environment, and suck up the biomass into their unproductive, wormy selves instead of letting it flow into the field crops. They also feed on the root systems. Cyst nematode resistance, by the way, is the second or third most popular line of genetic modification in soybeans.
This vulnerability to cyst nematodes is why nobody plants continuous soybeans, despite the attractiveness of a field crop which doesn’t require expensive nitrogen fertilizers. In the four years I've been in precision agriculture, I haven't found anyone doing this. There are a number of misguided Midwesterners who believe "continuous corn" planting practices will result in magical crop yields, but the nematode cyst issue keeps a similar "continuous soybean" myth from popping up. That this is the case, even though soybeans are massively cheaper to plant than corn, suggests to me that any such behavior in Argentina is no doubt vastly over-reported. Additionally, the most popular soybean varieties are short-season, and can be easily double-cropped in the more temperate climes. This lets the farmer plant soybeans in the summer, and a second crop of wheat or barley in the fall for a late spring harvest. They get two harvests a year from the same land, with still less fertilizer than what they’d have to use on a single-crop planting of corn. Double-cropping with a winter small grain allows the grower to cut down on the likelihood of a cyst nematode infestation. If an infestation develops anyways, the grower can just switch over to corn the next year and starve the cyst nematodes out.
Another bit of silliness is the worry about soybean plants going "rogue", or leaving behind second-year growths in the old field, or neighboring fields without the stigma of having nasty, nasty GM crops planted within their pristine borders. This sort of thing is actually a mild problem with corn or maize crops. If you drive by a field of soybeans in rotation with corn, you'll often see a few corn plants towering over the lowly soybean plants. Operative word being "towering". The soybean plant is not a particularly tall one. It is, in fact, somewhat dwarfish. It grows higher than timothy clover, and some of its fellow legumes, but in general, we're not talking "competitive threat" here. Wheat, cotton, barley, and corn plants all are much taller than even the most robust soybean plant. If your current crop can't out-compete a rogue soybean plant for light, water or nutrients, then you're doing something wrong, McDonald.
As a side-thought, the herbicides that Round-Up and the other, off-brand glyphosates have replaced are far, far more noxious than the glyphosates themselves, which break down rapidly in field conditions. Think chemical weaponry. The field hands would often have to make applications in full biogear. This is probably why the Greens hate the glyphosates so much. It's easy to freak out donors and politicians with Silent Spring scaremongering when the chemicals in question are actually pretty scary. You couldn't scare a cringing obsessive-compulsive neurotic with glyphosates, let alone somebody rational. Nothing irritates an activist more than a solution - it's a threat to their livelihood.